The recent findings that cannabinoids, in particular delta 9-tetra- hydrocannabinol (delta 9-THC), have immunosuppressive activity in humans and are highly active against solid tumors such as Lewis lung tumor, raise the possibility that these drugs may have beneficial therapeutic properties as anti-cancer agents. Preliminary observations indicate that during treatment with delta 9-THC normal cells will continue, after a short lag, to take up and incorporate H3-thymidine into their DNA whereas such incorporation shows a dose-dependent inhibition into the DNA of C3H mammary carcinoma. Experiments will therefore be carried out at the molecular level on DNA synthesis, chromosome damage, and the effect of delta 9-THC on embryogenesis, development and differentiation, using two model systems devised for such studies. Intact chromosomal DNA from Saccharomyces cerevisiae will be isolated and individual DNA molecules partially resolved. Incorporation of radioisotopes into these molecules, and any resultant breakage or damage of chromosomes in normal and known mutant cells following delta 9-THC treatment will be followed. Embryogenesis and patterns of differentiation and development in Volvox carteri are known, and mutations exist in which these controls have been disrupted, giving rise to abnormalities. The effect of delta 9-THC on both normal and abnormal patterns of development will be followed, and the differential effects of the drug, if any, determined. In this way any possibly detrimental effects of these potentially useful anti-cancer drugs will be readily detected early in their investigation, and a useful insight gained as to their possible mechanism of action.